It is known to those skilled in the art that, depending on whether high-frequency or low-frequency ultrasound is used, different effects can be obtained on fluids. In order to obtain mechanical effects, low frequencies (generally between 16 and 100 kHz) are regularly used.
These mechanical effects, which are due to cavitation, make it possible, for example, to mix, emulsify and disperse heterogeneous substances, to degas the liquids, etc. These mechanical effects also create high shear effects in the liquids, which makes it possible, for example, to disrupt living cells present in this medium, to the point of rupturing the walls of cells of this type.
These same mechanical effects are also used to clean surfaces by the action of the microjets of liquid produced by the implosion of the cavitation bubbles. Similarly, the fact that various reactants can be mixed very efficiently is advantageously used to promote diffusion phenomena in various chemical reactions, especially heterogeneous reactions.
If high frequencies are used, generally of between 300 kHz and several MHz, the cavitation phenomena become relatively less energetic and the mechanical effects are more reduced than when low frequencies are used.
By applying high-frequency ultrasound to a liquid medium, the lifetime of the cavitation bubbles produced is greatly reduced, and chemical phenomena in a homogeneous phase take place, which are radically different from those observed when lower frequencies are applied.
One parameter which is specific to the use of high-frequency ultrasound is that, despite the low mechanical energy required to degas the solutions, the effect obtained is greater than when low-frequency ultrasound is applied, which itself requires more power.